Amino acid sequence analysis has shown that many cellular proteins from sources as diverse as bacteria, archaea, fungi, plants, and animals, may be categorized into families or superfamilies. These categories may be based upon homologies within protein sequence alignments and between molecules which have similar biochemical characteristics and function. Some examples of these categories are 1) the immunoglobulin-like superfamily, 2) the protein kinase superfamily, 3) the P450 superfamily, 4) the TGF-.beta. superfamily, and 5) the hydroxysteroid dehydrogenase/dihydroflavonol reductase superfamily.
Constituents of the hydroxysteroid dehydrogenase/dihydroflavonol reductase superfamily are characterized by their common oxidoreductase activity upon polycyclic aromatic compounds. In general, the activity either oxidizes a hydroxyl group to a ketone with nicotinamide adenine dinucleotide (NAD.sup.+) coenzyme or reduces a ketone group to an alcohol with nicotinamide adenine dinucleotide phosphate (NADPH) coenzyme as the hydrogen donor (Baker, M. E. et al. (1990) Biochem. J. 269:558-559). The superfamily has now been extended to include bacterial cholesterol dehydrogenase and UDP-galactose-4-epimerase. Members of the superfamily are believed to be derived from an ancestral protein which metabolized sugar nucleotides (Baker, M. E. and Blasco, R. (1992) FEBS Lett. 301:89-93).
Despite the apparent biochemical difference between vertebrate steroid precursors and flavonoid precursors in plants, regulation of eukaryotic gene transcription is a functional thread common to members of the superfamily. Of further interest is the role of plant flavonoids in intracellular communication between plants and rhizobia (Baker, et al. (supra)).
The strongest homologies between members of the steroid dehydrogenase/dihydroflavonol reductase superfamily lie within the N-terminal region of the enzymes. This region contains a putative NAD(P)(H)-binding motif and other motifs present in short chain alcohol dehydrogenase active sites (Scrutton N. S. et al. (1990) Nature 343:38-43; PROSITE: PDOC00060, SWISSPROT, Geneva, Switzerland).
The polyketide antibiotic actinorhodin is produced by Streptomyces coelicolor as a secondary metabolite. The actinorhodin biosynthetic pathway has been extensively characterized, and the gene cluster encoding the metabolic enzymes has been isolated and fully sequenced (Kendrew, S. G. et al. (1997) J. Bacteriol. 179:4305-4310).
Actinorhodin is a homodimer of a tricyclic aromatic compound which undergoes extensive chemical modification prior to dimerization. One gene within the gene cluster, actVA-ORF4, has unknown function, but it is believed to mediate ring hydroxylation and subsequent oxidation/dehydrogenase reactions at position C-6 (Femandez-Moreno, M. A. et al. (1994) J. Biol. Chem. 269:24854-24863). This reaction would require the transfer of a hydrogen ion from an enzyme or coenzyme. The N-terminal one-third of actVA-ORF4 shows a resemblance to the N-terminus of the plant dihydroflavonol reductases (Caballero, J. L. et al. (1991) Mol. Gen. Genet. 230:401-412).
Evaluation and characterization of a porcine small intestine cDNA library has revealed the presence of an expressed sequence tag clone, SSC2H07, which encodes an open reading frame of 135 residues (SSC2H07 ORF gene product; Winter.o slashed., A. K. et al. (1996) Mamm. Genome 7:509-517). Functional analyses of many mammalian proteins suggest that higher animals synthesize peptides that have antibiotic activity, particularly in the gut epithelium (Porter, E. M. et al. (1997) Infect. Immun. 65:2389-2395). No compounds that resemble bacterial antibiotics have been reported to be synthesized in higher animal tissue.
The discovery of a new actVA-ORF4-like protein and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention, and treatment of infectious, vesicle trafficking, immunological, and neoplastic disorders.